Translucency/opaque sorting

ABSTRACT

A method and apparatus for sorting particles according to the degree of transparency thereof wherein the particles are passed seriatim through a viewing zone or chamber and are illuminated therein from one side to produce a shadow pattern on a plurality of photosensors opposite the illuminating source. The photosensors scan across the shadow pattern a plurality of times as the particles pass through the viewing zone. The photosensors in &#39;&#39;&#39;&#39;gray&#39;&#39;&#39;&#39; areas of the shadow pattern produce one signal and photosensors in &#39;&#39;&#39;&#39;black&#39;&#39;&#39;&#39; areas of the shadow produce a second signal. Each type of signal is counted and the counts are integrated as multiple scans are made across the moving shadow pattern to give an indication of the relative gray and black areas in the shadow pattern. Particles whose black areas exceed gray areas by a predetermined amount are sorted from the remainder of the particles whose black areas are less than the gray areas by a predetermined amount.

United States Patent 11 1 Muehlethaler 1 June 17, 1975 l 54 l TRANSLUCENCY/OPAQUE SORTING Urs Muehlethaler, Gerlafingen, Switzerland [75] Inventor:

[73] Assignee: Sortex Company of North America,

Inc., Lowell, Mich.

[22] Filed: Dec. 14, 1973 [21] Appl. No.: 424,729

[52] U.S. Cl 209/lll.7; 250/222 R; 250/563 [51] Int. Cl. 1307c 5/342 [58] Field of Search 209/1 11.7, 111.6;

Primary Examiner-Allen W. Knowles Attorney, Agent, or Firm-McGarry & Waters 57 ABSTRACT A method and apparatus for sorting particles according to the degree of transparency thereof wherein the particles are passed seriatim through a viewing zone or chamber and are illuminated therein from one side to produce a shadow pattern on a plurality of photosensors opposite the illuminating source. The photosensors scan across the shadow pattern a plurality of times as the particles pass through the viewing zone. The photosensors in gray" areas of the shadow pattern produce one signal and photosensors in black" areas of the shadow produce a second signal. Each type of signal is counted and the counts are integrated as multiple scans are made across the moving shadow pattern to give an indication of the relative gray and black areas in the shadow pattern. Particles whose black areas exceed gray areas by a predetermined amount are sorted from the remainder of the particles whose black areas are less than the gray areas by a predetermined amount.

13 Claims, 7 Drawing Figures L'J cf. PATENTEU 17 .u go ,221 SHEET 2 24* POWER SUPPLY LAMP +7 \NVERTER f +5 +9 +24 +29 STROBE 58 56 PHOTO season a scANNme CLOCK 9 DRWER BOARD ARRAY 4 INTERFACE swasrm so 62. T 64 VIDEO g AMPLIFIER mv,

AND COUNTER mscamm 66 us l \J I GRAY+ I42.

COMPARATOR PROGRAMABLE 4 DWlDER :8 ,-1

COUNTER 16 92 DELAY D? CLOCK mmcAwR BB m-zsus'rsa so DECISION 4p AND PuLsE 96 RESET LENGTH ms CONTROL PULSE 84 SHAPER ssscwoa l DRWER FIG. 5

PATENTEDJUH 1 7 I975 SHEET 1 TRANSLUCENCY/OPAQUE SORTING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to sorting particles according to the ability of the particles to pass light. In one of its aspects, the invention relates to a method and apparatus for sorting transparent or partially transparent particles from opaque particles. In another of its aspects, the invention relates to a method and apparatus for sorting particles according to their degree of transparency.

2. Background of the Invention In commonly assigned co-pending U.S. patent application Ser. No. 347,184. entitled REFUSE SORTING AND TRANSPARENCY SORTING, now U.S. Pat. No. 3,802,558. there is disclosed and claimed a method and apparatus for sorting refuse according to its components wherein opaque particles such as stones, crockery, ceramics, etc., are unavoidably contained in a resulting glass-rich fraction. The opaque particles are sorted from the glass particles by measuring the transparency of the particles passing through a viewing zone and sorting the particles according to the measured transparency thereof. As described in the application, each particle produces a shadow pattern on a strip of photosensors, for example, photodiodes, as the particles pass between a strip light source and the strip of photosensors. The shadow pattern includes a central black area and side gray areas for opaque particles and includes a central gray area and possibly side black areas for glass particles. The size of the black area or areas is measured and the particles are sorted according to the ratio of black to non-black areas,

SUMMARY OF THE INVENTION According to the invention, there is provided a method and apparatus for sorting particles according to the degree of transparency of the particles wherein both gray and black areas are measured and the ratio of black to gray areas is used to sort the particles. The particles are passed by suitable means seriatim through a viewing zone or chamber and are illuminated therein, preferably by a strip light source, at one side of the viewing zone or chamber. A shadow pattern is produced on a surface in the viewing zone or chamber opposite the illumination source. At least some of the particles produce a shadow pattern having black areas or a first level of light attenuation and gray areas, or a second level of light attenuation. The two levels of light attenuation are measured and the ratio of the black to gray areas is computed. The particles are thereafter sorted according to the ratio of black to gray areas, or vice versa. For example, those particles which produce a shadow pattern with a black area in excess ofa predetermined percentage of the gray area are sorted from the remainder of the particles.

Desirably, the measuring means comprises a strip of photosensors which are aligned to receive the light from a strip light source. The photosensors are scanned at a high frequency so that multiple scans are made across the shadow as the shadow moves across the strip light source. The signals from each of the photosensors are representative of the degree of light attenuation and of the signals for the respective gray areas and black areas are integrated to produce a composite comparison between the gray and black areas for each particle.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings in which:

FIG. I is a side elevational view in section schematically illustrating a sorting apparatus according to the invention;

FIG. 2 is a plan view in section taken along lines 22 of FIG. 1;

FIG. 3 is an enlarged plan view schematically showing effect of an opaque particle passing through the sorting apparatus;

FIG. 4 is an enlarged plan view similar to FIG. 3 but schematically showing the effect of a glass particle passing through the sorting apparatus;

FIG. 5 is a schematic block diagram of an electrical system for operating the sorting apparatus; and

FIG. 6 is a schematic electrical diagram of an amplifier and discriminator used in the electrical system according to the invention.

FIG. 7 is a schematic representation of the wave form of the video signal from the scanning array.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and to FIGS. 1 and 2 in particular, the transparency sorting apparatus comprises a housing 12, open at both top and bottom to allow particles 26 to pass freely therethrough. The par ticles are fed seriatim from a suitable feeding device (not shown) to the top of the housing I2. Suitable feeding devices include belt feeds and chutes and are well known in the art of photoelectric sorting. Examples of suitable feeding devices are disclosed in Fraenkel U.S. Pat. No. 3,197,647, and in Rayment U.S. Pat. No. 3,513,956.

A strip light source 14, such as a fluorescent tube, is mounted in a darkened box 15 within the housing 12 in back of a mask 16 having a slot opening 18. A lens 20, mounted on a holder 21, is supported across the housing from the light source 14 to focus the light passing through the slot 18 onto a linear array of photosensors 22. An air ejector 24 is mounted beneath the housing 12 to deflect the trajectory of the particles 26 under certain conditions to be described hereinafter. The photosensors 22 preferably comprise an array of photodiodes adapted to sense the intensity of the light from the light source. The photosensors 22 are separate sensing units which are programmed to scan across the slot 18 and report the intensity received at each photosensor in a sequential manner. Such a programmed array of photodiodes are well-known, as, for example the IPL 7000 series sold by IPL (Integrated Photomatrix Ltd.) of Dorchester, Dorset, U.K. The array of photodiodes gives a high resolution of light intensity across the slot 18. Thus, the photodiodes are suitably adapted to resolve the transparent characteristics of particles passing between the photodiodes and the slot 18.

The number of photosensors in the array will depend on the resolution desired and the length of the slot I8. The size of the particles 26 will determine the length of the slot 18. If, for example, the particles are in the range of one-fourth to three-fourths of an inch, the slot length will be about 1% inches long. For such a slot length, a photosensor array of about 32 units would be suitable. For purposes of simplicity, only a few of such sensors have been schematically represented in the drawings.

In lieu of the fluorescent light source I4 and mask 16, there can be provided a collimated strip of light from a remote cold high intensity light source transmitted through a fiber-optic light guide. Fiber-optic light guides are well-known, for example, the type sold by American Optical Corporation.

Reference is now made to FIG. 3 wherein there is shown schematically the effect of an opaque particle passing between the light source and the photosensor array. The opaque particle 26 passing between the light source I4 and the array ofphotosensors 22 would provide a particular light pattern on the photosensor. A shadow will be cast by the opaque particle 26 onto an area 30 of the photosensor array. On either side of the shadow area 30 there will be portions 28 of full light and portions 32 of partial shadow between the shadow area 30 and the light portions 28. The partial shadow areas are a result of light rays from the light source directed angularly from the light source past the edge of the particle. Thus, in any given scan by the photosensor array when a particle 26 is passing through the viewing area, certain of the photosensors will report full light, certain of the photosensors will report partial light, and other photosensors will report darkness or shadow.

The effect of a glass particle passing in front of the photosensors 22 is illustrated in FIG. 4 to which reference is now made. The glass particle 22 may have a fa cial area 36 and side edges 38 and 40 which are disposed at an acute angle to the facial area 36. These side edges 38 and 40 may appear translucent or even opaque to the photosensors due to reflection of the light from internal surfaces thereof. Thus, as a scan is made across the array of photosensors with the glass particle 92 in front of the photosensors, the photosensors in areas 42 will report full light whereas the photosensors in area 46 will sense somewhat attenuated light depending on the color of the glass particle 34. The photosensor in areas 44 will sense darkness or near darkness compared to the photosensors in areas 46 and 42. For a piece of flint glass, the area 46 will report a gray area and attenuated as compared with the white areas 42. For a brown or green piece of glass, the area 46 will report a gray area somewhat darker than that of flint glass but of somewhat lighter intensity than the shadow area 32 of FIG. 3.

As will be evident from the foregoing, opaque particles 26 and glass particles 34 both produce areas of shadow and partial shadow. Thus, a true sorting of opaque particles from partially transparent particles can not be made solely on the basis of whether or not dark areas or shadow areas appear at the photosensors. Further, since both types of particles produce partial shadow areas. sorting can not be predicated on whether partial shadow areas are present. According to the present invention, sorting is based on the ratio of partial shadow areas to full shadow areas, or visa versa.

An electrical system for obtaining the ratios and distinguishing between opaque and transparent particles is illustrated in FIG. to which reference is now made. A power supply 50 is coupled to a lamp inverter 52 which drives the light source 14. The power supply is also coupled to a photosensor scanning array 54 which contains the photosensors 22. The scanning array 54 desirably is a linear array of silicon planar photodiodes integrated with a dynamic M.O.S. shift register on a monolithic chip. Multiplexing and amplifying M.O.S. devices are connected to each diode to interrogate each diode in sequence responsive to an input pulse propagated through the register to produce a single serial video output signal. Each diode produces an output pulse representative of the light intensity of the diode at the time the diode is interrogated. The output signal will thus be a series of pulses related to the light intensity at each of the diodes. Since the normal condition of the diodes is full light, the diodes do not report when there is full light. In other words, the pulses will represent the shadow and partial shadow areas seen by the photodiodes as a particle falls between the light source and the photodiodes. For purposes of simplicity, pulses generated by areas of partial shadow will be referred to as gray pulses" and pulses produced from full shadow areas will be referred to as black pulses. Further, the areas of partial shadow will be referred to as gray areas and the areas of full shadow will be referred to as *black" areas. The integrated scanning array can be purchased as a unit, for example, as an IPL 7000 series from Integrated Photomatrix Ltd. of Dorchester, Dorset, UK

The scanning array 54 is driven by a scan clock driver 58 through a clock interface 56. Scan clock driver circuits are well-known for driving scanning arrays and thus will not be described in detail for the sake of brevity. The scan clock driver 58 produces a scan start signal at a predetermined frequency and applies the scan start signal to the scanning array 54 through the clock interface 56. The function of the clock interface is to raise the amplitude of the signal from the clock driver to a proper level for feeding to the scanning array. The scan clock driver 58 also applies signals to the scanning array 54 to regulate the rate at which the scanning array will scan across the photosensors. Normally, the scanning array 60 will be bistable so that two signals, with respect to each other, are applied to scanning array.

A strobe signal is also produced by the scan clock driver 58 representative of the frequency of the clock pulses. The strobe signal has a frequency equal to that at which information is received from each photosensor.

The output from the scanning array 54 is illustrated schematically in FIG. 7. Any video signal will have an intensity of V such as, for example, 24 volts and any areas of attenuated light will have a lesser voltage. For example, white glass would result in a voltage of about 2O/2 volts and green or brown glass would result in a voltage of 19% volts. Each diode which sensed the white, green or brown glass would have a voltage V as seen in FIG. 7. Similarly any areas of partial shadow as, for example, areas 32 of FIG, 3 would also be represented by V in FIG. 7. Any black areas and shadows such as areas 30 in FIG. 3 or areas 44 in FIG. 4 would be represented by V in FIG. 7 and would, for example, have a voltage of about l9 volts or less.

Referring now again to FIG. 5, the video signal from the photosensor scanning array 54 is fed to the video amplifier and discriminator 60. The video signal from the scanning array will consist of a number of pulses which may have different amplitudes. One value of amplitude will represent black pulses and another value or group of values of amplitude will represent gray pulses. The video amplifier and discriminator detects the number of black pulses and produces an output signal representative of the number of black pulses in any given scan. The output signal is merely a number of black pulses. This signal is applied to a counter 64 through a divider 62. The number of black pulses is divided by two in the divider 62 by a conventional flip-flop or other similar mechanism. The counter 64 counts the number of pulses applied thereto and produces a digital signal representative of the number of black pulses, which signal is applied to comparator 66.

The video amplifier and discriminator 60 detects the number of gray pulses in the video input signal and produces an output signal representative of the number of pulses in the discriminator. This output signal representative of the gray pulses is also in the form of a number of pulses and is applied to a programmable divider 68 having a selector switch 70. The divider 68 divides the number of pulses applied thereto by one of a plurality of selected numbers and produces an output signal representative of the quotient. The divider, for example, can be programmed to divide the pulses by four, five, six or eight so that the output therefrom is a signal representative of one-fourth, one-fifth, one-sixth or oneeighth of the input signal. The selection is made by the selector switch 70. The output from the programmable divider 68 is applied to counter 72 which counts the input gray pulses and produces a digital signal representative of the number of pulses applied thereto. This digital signal is applied to comparator 66. The digital number applied to the comparator by the counter 64 is compared with the digital number applied by the counter 72 and an output signal results if the number applied by the counter 64 is greater than the number applied by the counter 72. A gray counter 74 which comprises a light emitting diode, is coupled to an output of counter 72 to give a visual indication of any signals representative of gray signals for any given scan.

Referring again now to FIG. 5, the output from the comparator 66 is fed to AND gate 76 which is open when a signal is applied from a decision and reset control circuit 88. Thus, when AND gate 76 is open, the signal from comparator 66 is applied to delay shift register 78 which delays the signal and applies the delayed signal to an adjustable pulse length monostable circuit 82 having an adjustable potentiometer 84. The output signal from the pulse length monostable circuit 82 is applied to an ejector drive 86 which operates the air ejector 24. An adjustable delay clock 80 is coupled to the delay shift register 78 to time the delay applied to the signal in the delay shift register 78.

The decision and reset control 88 receives a scan start signal from the scan clock driver as a measure of the start of each scan across the photosensors. A signal representative of gray pulses from the video amplifier and discriminator 60 is also applied to the decision and reset control 88. The decision and reset control senses the first and only the first scan without a gray pulse, i.e. signal from the video amplifier and discriminator 60 representative of the gray reporting photosensors. and generates an output decision signal responsive to such a scan. The output decision signal from the decision and reset control 88 is applied to the programmable divider 68 to the divider 62 and to the counters 64 and 72 to reset each of these circuits. At the time the reset signal is applied to the counter circuits, a gating signal is also applied to AND gate 76 and to an indicator latch 90. The signal to AND gate 76 allows the output signal from the comparators 66 to pass to the delay shift register 78 as described above.

The indicator latch 90 is also coupled to the output from the comparator 66 to receive a signal in the event that the gray pulses exceed the black pulses. A visual indicator 92 such as a light emitting diode, is coupled to the indicator latch 90 to light up when there is no signal from the comparator 66. Similarly, a visual indicator 94, such as a light emitting diode, is coupled to the indicator latch 90 to light up when a signal is received from the comparator 66. The indicator latch serves as a latching device and gate to illuminate the indicators 92 and 94 responsive to a signal (or absence ofa signal) from the comparator and responsive to a signal from the decision and reset control 88. In other words, the output from the comparator 66 is applied continuously to the indicator latch 90 but is inoperative to illuminate the indicators 92 or 94 until a signal is received from the decision and reset control 88. Upon receipt of such a signal, the illuminator 92 will be illuminated if there is no signal from the comparator 66 and the indicator 94 will be illuminated if a signal is received from the comparator 66. The latch 90 maintains the indicator 90 or 94 in an on position until a new signal is applied from the decision and reset control 88. The indicator 74 can be used to determine whether there is dirt or other foreign matter in front of the photosensors.

The pulse shaper 96 having a manual switch 98 is coupled to the indicator latch 90 and to the delay shift register 78 to manually test the ejector system. The pulse shaper 96 is also coupled to the decision and reset control 88 to reset the counters after each actuation of the pulse shaper 96.

Reference is now made to FIG. 6 for a description of the video amplifier and discriminator circuit 60. A video input line 100 from the photosensor scanning array 54 (FIG. 5) is applied to the inverting input of a comparator 104 through a resistor 102. The comparator 104 compares the voltage of each pulse in the signal with a preset voltage applied to the non-inverting input of the comparator 104 and produces an output signal if the voltage of any given pulse is withinn a specified range as, for example 19 /2 to 21 volts. THe output of comparator 104 is attenuated in resistor 106 and am plified in transistor 108, and applied to NAND gate 114. A filter circuit of a capacitor 110 and a resistor 112 controls the amplitude of the signal applied to NAND gate 114 by the amplifier 108. The strobe signal is applied to NAND gate 114 through line 142. The strobe signal is generated by the scan clock driver 58 and represents the frequency of the clock pulse. when the strobe signal 142 is applied to NAND gate 114, the gate will open when a pulse representing a gray signal from a photodiode is applied to the gate. An output signal from NAND gate 114 is applied to terminal 116 which in turn is applied to the programmable divider 68 (FIG. 5). A voltage line 118 having, for example, a voltage of 29 volts is applied to the non-inverting input to the comparator through resistor 120. A lesser voltage line 122, containing, for example, 9 volts, is also applied to the non-inverting input of the comparator 104 through a clamping diode 124. Capacitors 143 and 136 are connected between a ground line 128 and a positive input to the comparator 104. Voltage lines 138 and 140, containing, for example, l5 and 5 volts respectively, are applied to the comparitor to provide power for the comparitor 104. Resistor 126 is provided between ground line 128 and the inverting input to the comparator 104. In a similar manner. potentiometer 130 having an adjustable slide 132 is provided between the noninverting input to comparator 104 and the ground line 128. Normally, the potentiometer 130 is set at a predetermined value so that gray pulses representing either flint glass or green or brown glass are detected by the comparator. However, as indicated above, the voltage representative of green and brown glass will be somewhat less than the voltage representative of the flint glass. Thus, the potentiometer 130 can be set so as to sort the flint glass from the green and brown glass. This color sorting can take place by simply raising the level at which the comparator will produce an output signal to thereby eliminate the green and brown glass from the gray pulses.

A similar circuit is provided for developing pulses re lating to the black pulses. The video signal in line 100 is applied to the inverting input of comparator 146 through resistor 144. A resistor 160 is provided between the ground line 128 and the inverting input of comparator 146. Voltages from voltage lines 188 and 140 are also applied to the comparator 146 to provide power therefor. The non-inverting input to the comparator 146 is provided by voltage line 122 through clamping diode 168. A capacitor 170 is provided between voltage line 140 and the non-inverting input to comparitor 146. Further, potentiometer 164 having slider [66 is provided between the ground line 128 and the input to comparator 146. The slider 166 on potentiometer 164 adjusts the level at which black pulses are sensed by the comparator 146.

The output from comparator 146 is amplified by transistor 150 after being attenuated by resistor 148 and the signal is thereafter applied to NAND gate 152 which is strobed with a signal from strobe line 142. Filter circuits including capacitor 156 and resistor 158 control the amplitude of the signal to NAND gate 152. THe output from NAND gate 152 is applied to the black output terminal 154 which is coupled to divider 62 (FIG.

The amplifier and discriminator circuit operates as follows: The video signal containing pulses representative of gray and black areas as seen by the photosensors is applied to the video input line 100. Gray pulses representing individual photosensors within any gray area and having a voltage in the range of about 19% to 2l volts, triggers the comparator 104 to produce pulse signals at gate 114. Those pulses having a voltage of l9 volts or below trigger the comparator 146 to produce pulse signals at gate 152. Thus, each pulse in the video signal having a voltage in the range of 19 /2 to 21 will give rise to a signal at gate 114. Similarly, each pulse in the video signal having a voltage of 19 volts or below will give rise to a signal at gate 152. The NAND gates 152 and 114 will respond to the gray and black pulses as strobe signals are applied thereto so that the gray and black pulses are applied to the respective terminals 154 and 116.

OPERATION The operation of the entire sorting apparatus will now be described with reference to FIGS. 3, 4 and 5. As the particles are fed to the viewing zone, they pass between the light source 14 and the array of photosensors 22. As the scanning array 54 scans the photosensors, it produces an output video signal having pulses relating to the areas of darkness (black pulses) and the areas of grayness (gray pulses). This video signal is applied to the video amplifier and discriminator 60 which separates the black pulses from the gray pulses. Thus, the black pulses are applied to the divider 62 which divides the black pulses by two (or any other suitable number) and applies the quotient to counter 64. The gray pulses are applied to the programmable divider 68 wherein the number of pulses is divided by an integer such as four, five, six. or eight. The quotient is thereafter applied to the counter 72. The scanning array 54 operates at a high frequency. for example 3.340 cycles per second, so that a number of scans are made across each particle as it falls through the viewing zone. The counting process continues for the entire time that a particle passes through the light sensitive area. The total number of pulses representing black areas for successive scans across any given particle, are applied to counter 64. Likewise, the total number of pulses representing the gray areas in successive scans are applied to the counter 72. As soon as there is a complete scan across the photosensors without any gray pulses, the decision and reset control will reset the dividers 62 and 68 and the counters 64 and 72. The comparator will have an output signal if the number of pulses applied by counter 64 exceeds the number applied by counter 72 and that signal will be simultaneously applied to the delay shift register 78 which in turn, after a delay, causes the pulse length monostable to drive the ejector to eject the particle.

If the number of gray pulses are divided by four, for example, and the pulses applied from counter 64 exceed those pulses applied from counter 72, then the black pulses comprise more than 50 percent of the gray pulses. In other words, on an integrated basis for any particle, the area 30 of FIG. 3 would be greater than 50 percent of the total area in area 32. With respect to FIG. 4 the areas 44 of FIG. 4 would be more than 50 percent of the area 46. In a similar manner, if the gray pulses are divided by 5, the black pulses would represent at least 40 percent of the gray area before a signal is applied by the comparator. 1f the gray pulses are divided by six, the black pulses would reach at least 33 percent of the gray areas before a signal is applied from the comparator 66 and if the gray puises are divided by eight, the black pulses would be at least 25 percent of the gray pulses before a signal is produced by the comparator 66.

Thus, if the gray pulses counted by the counter 72 exceed the black pulses counted by the counter 64, no signal is applied to gate 76 and the ejector is thus not driven. Therefore, all particles falling below the predetermined ratio of black to gray pulses will continue on their trajectory path through the viewing zone and the particles which produce a ratio of black to gray pulses in excess of the predetermined ratio will cause driving of the ejector to deflect the particles to a reject bin.

The comparitor 66 also produces a signal when the gray counts exceed the black counts and that signal is fed to the indicator latch 90. Upon receiving the signal from the comparator. the indicator latch will operate the indicator 94 upon receiving the pulse signal from the decision and reset control 88 and will maintain that indicator on until it receives another pulse signal from the decision and reset control 88. [f the black pulses exceed the gray pulses, no signal will be applied to the indicator latch 90 and upon receipt of the pulse signal from the decision and reset control 88, the indicator 90 will be turned on and held on until another pulse is received from the decision and reset control 88.

Thus. in summary. the sorting apparatus operates to eject or reject all particles which produce a shadow pattern wherein darker areas of the pattern exceed a predetermined percentage of the lighter areas. This apparatus can be used for sorting opaque particles from transparent particles and from sorting particles according to their translucent and opaque characteristics. The sorting apparatus and method of the invention sorts particles according to the degree of transparency or transparent particles from opaque particles regardless of the size of the particles.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, drawings, and appended claims without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of sorting particles according to their degree of transparency comprising the steps of:

passing each particle seriatim through a viewing zone;

illuminating one side of the particles to produce a shadow pattern on a surface in said viewing zone, the shadow pattern of at least some particles having a first area of a first level of light attenuation and a second area of a second level of light attenuation different from said first level, each of said first and second areas being less than the total area of the shadow pattern of said particles,

measuring the relative sizes of the first and second areas of light attenuation; and

sorting those particles which produce a shadow pattern whose ratio of first area to second area exceeds a predetermined value from other particles whose shadow pattern produces a ratio below the predetermined value.

2. A method of sorting particles according to claim 1 wherein the first and second areas are measured by taking repeated scans across the shadow pattern of each particle as the particle passes through the viewing zone.

3. A method of sorting particles according to claim 2 wherein the particles pass in a free-fall manner through the viewing zone.

4. A method of sorting particles according to claim 1 wherein the respective areas of first and second levels of light attenuation are measured by scanning across each shadow pattern a plurality of times as the particle passes through the viewing zone, the width of each of the first and second areas is detected during each scan and the detected width of each scan is integrated to give a value of each area of each particle.

5. An apparatus for sorting particles according to the degree of transparency thereof comprising in combination:

means for passing each particle seriatim through a viewing means;

means for illuminating one side of each particle in said viewing means to produce a shadow pattern on a surface in the viewing means. the shadow pattern of at least some particles having a first area of a first level of light attenuation and a second area of a second level of light attenuation different than the first level, each of the first and second areas of light attenuation being less than the total area of the shadow pattern of said particles;

means for measuring the relative size of the first and second areas of light attenuation for each particle in the viewing means; and

means for sorting each particle which produces a shadow pattern whose ratio of first area to second area exceeds a predetermined value for other particles which produce a shafow pattern whose ratio of first to second area is below the predetermined value.

6. An apparatus according to claim 5 wherein the passing means delivers the particles in a free-fall manner to the viewing means.

7. An apparatus for sorting particles according to claim 5 wherein the illuminating means includes a strip light source.

8. An apparatus for sorting particles according to claim 7 wherein the measuring means comprises a strip of photosensors aligned to receive light from the strip light source.

9. An apparatus according to claim 5 wherein the measuring means comprises a strip of photosensors aligned to receive light from the illumination means.

10. An apparatus for sorting particles according to claim 9 wherein the measuring means further comprises means to scan across the strip of photosensors, each photosensor producing an output signal representative of the value of light received thereby at the time of each scan, and means for counting the output signals representative of the first level of light attenuation and the output of signals representing the second level of light attenuation; and means for comparing the number of signals representative of the first level of light intensity to the number of signals representative of the second level of light intensity.

11. An apparatus for sorting particles according to claim 10 wherein the comparing means further includes means for integrating the number of signals representative of all photosensors reporting the first level of light attenuation on a plurality of scans as the particle passes through the viewing zone, and for integrating the signals representative of all photosensors reporting the second level of light attenuation on a plurality of scans across the photosensors as the particle passes through the viewing zone; means for operating said sorting means responsive to the integrated ratio of the first level of light attenuation signals to the second level of light attenuation signals.

12. An apparatus for sorting particles according to claim 11 and further comprising means to divide the number of signals representative of the second light intensity.

13. An apparatus according to claim 10 and further comprising means to divide the number of signals representative of the second light intensity. 

1. A METHOD OF SORTING PARTICLES ACCORDING TO THEIR DEGREE OF TRANSPARENCY COMPRISING THE STEPS OF: PASSING EACH PARTICLE SERIATIM THROUGH A VIEWING ZONE; ILLUMINATING ONE SIDE OF THE PARTICLES TO PRODUCE A SHADOW PATTERN ON A SURFACE IN SAID VIEWING ZONE, THE SHADOW PATTERN OF AT LEAST SOME PARTICLES HAVING A FIRST AREA OF A FIRST LEVEL OF LIGHT ATTENUATION AND A SECOND AREA OF A SECOND LEVEL OF LIGHT ATTENUATION DIFFERENT FROM SAID FIRST LEVEL, EACH OF SAID FIRST AND SECOND AREAS BEING LESS THAN THE TOTAL AREA OF THE SHODOW PATTERN OF SAID PARTICLES, MEASURING THE RELATIVE SIZES OF THE FIRST AND SECOND AREAS OF LIGHT ATTENUATION; AND SORTING THOSE PARTICLES WHICH PRODUCE A SHADOW PATTERN WHOSE RATIO OF FIRST AREA TO SECOND AREA EXCEEDS A PREDETERMINED VALUE FROM OTHER PARTICLES WHOSE SHADOW PATTERN PRODUCES A RATIO BELOW THE PREDETERMINED VALUE.
 2. A method of sorting particles according to claim 1 wherein the first and second areas are measured by taking repeated scans across the shadow pattern of each particle as the particle passes through the viewing zone.
 3. A method of sorting particles according to claim 2 wherein the particles pAss in a free-fall manner through the viewing zone.
 4. A method of sorting particles according to claim 1 wherein the respective areas of first and second levels of light attenuation are measured by scanning across each shadow pattern a plurality of times as the particle passes through the viewing zone, the width of each of the first and second areas is detected during each scan and the detected width of each scan is integrated to give a value of each area of each particle.
 5. An apparatus for sorting particles according to the degree of transparency thereof comprising in combination: means for passing each particle seriatim through a viewing means; means for illuminating one side of each particle in said viewing means to produce a shadow pattern on a surface in the viewing means, the shadow pattern of at least some particles having a first area of a first level of light attenuation and a second area of a second level of light attenuation different than the first level, each of the first and second areas of light attenuation being less than the total area of the shadow pattern of said particles; means for measuring the relative size of the first and second areas of light attenuation for each particle in the viewing means; and means for sorting each particle which produces a shadow pattern whose ratio of first area to second area exceeds a predetermined value for other particles which produce a shafow pattern whose ratio of first to second area is below the predetermined value.
 6. An apparatus according to claim 5 wherein the passing means delivers the particles in a free-fall manner to the viewing means.
 7. An apparatus for sorting particles according to claim 5 wherein the illuminating means includes a strip light source.
 8. An apparatus for sorting particles according to claim 7 wherein the measuring means comprises a strip of photosensors aligned to receive light from the strip light source.
 9. An apparatus according to claim 5 wherein the measuring means comprises a strip of photosensors aligned to receive light from the illumination means.
 10. An apparatus for sorting particles according to claim 9 wherein the measuring means further comprises means to scan across the strip of photosensors, each photosensor producing an output signal representative of the value of light received thereby at the time of each scan, and means for counting the output signals representative of the first level of light attenuation and the output of signals representing the second level of light attenuation; and means for comparing the number of signals representative of the first level of light intensity to the number of signals representative of the second level of light intensity.
 11. An apparatus for sorting particles according to claim 10 wherein the comparing means further includes means for integrating the number of signals representative of all photosensors reporting the first level of light attenuation on a plurality of scans as the particle passes through the viewing zone, and for integrating the signals representative of all photosensors reporting the second level of light attenuation on a plurality of scans across the photosensors as the particle passes through the viewing zone; means for operating said sorting means responsive to the integrated ratio of the first level of light attenuation signals to the second level of light attenuation signals.
 12. An apparatus for sorting particles according to claim 11 and further comprising means to divide the number of signals representative of the second light intensity.
 13. An apparatus according to claim 10 and further comprising means to divide the number of signals representative of the second light intensity. 